The destructive power of ammonium nitrate (AN) has been graphically demonstrated in a number of malicious attacks including the more widely known instances of the Alfred P. Murrah Federal building in Oklahoma City and the J.W. Marriott Hotel in Jakarta. AN mixed with fuel oil or with a catalyst such as aluminum powder creates a powerful explosive, which is often a weapon of choice for acts of terrorism. Despite its critical role in agriculture, AN has become a vehicle for spreading chaos and an ominous threat to modern society.
According to data published by the Joint Improvised Explosive Device Defeat Organization (JIEDDO), over 80% of the improvised explosive devices (IEDs) and home-made explosives (HMEs) deployed in Afghanistan in 2011 use AN as the explosive precursor. The manufacture of AN is prohibited in Afghanistan but is marketed in neighboring Pakistan as calcium ammonium nitrate (CAN), a mixture of water soluble AN and insoluble calcite (limestone) or dolomite. As marketed, CAN is typically a 4 to 1 prilled or granulated blend of ammonium nitrate and calcite or dolomite. CAN is somewhat less sensitive to detonation than pure AN but can be converted to an explosive with minimum effort. The two most common approaches for converting CAN into a bomb precursor is to simply crush it to increase its surface area/reactivity or to extract it with water followed by evaporative re-concentration of the ammonium nitrate. These two routes for making HME's require minimal sophistication and rely on readily available materials/equipment; i.e., sausage mills, diesel, aluminum, powdered sugar, etc. Furthermore, in addition to being readily converted into an explosive, CAN is easily hidden in any variety of packaging configurations and is essentially non-detectable by stand-off equipment or canines. The proposed fertilizer reformulation set forth in this document prevents the crushing or extraction of CAN to make an IED/HME while simultaneously using odorants to render it detectable by smell without the need for sophisticated detection equipment.
Urea is a commonly used alternate source of nitrogen in agriculture. However, CAN or AN is generally preferred due to improved and prolonged response of many field crops to nitrate nitrogen. Further, depending on soil moisture, temperature, and bacterial activity, urea is prone to volatile losses of nitrogen as ammonia gas making the timing of field application of urea more critical than for CAN.
Commercial-grade urea contains about 44% available nitrogen versus about 27 wt % nitrogen in CAN meaning that combining urea and CAN yields a product with a total nitrogen content greater than that of CAN. However, combining urea with CAN yields a highly hygroscopic mix that immediately begins to absorb atmospheric moisture, even in semi-arid conditions (i.e., the combination has a low critical relative humidity).
Absorption of water by the mixture of urea and AN or urea and CAN may be avoided by applying a thick coating to the urea or to the AN or CAN granules to prevent contact between the urea and the ammonium nitrate components: An attempt to increase detonability by crushing eliminates this barrier allowing the AN/urea or CAN/urea to interact and convert to a non-detonable slurry. Likewise, unlike the water-insoluble limestone component of CAN, the AN cannot be purified by aqueous extraction since both urea and AN are water soluble.
The platform for the detection and defeat of IED/HMEs set forth in this document entails coating urea and/or the nitrate fertilizer with gypsum or other agriculturally-compatible material and then blending the urea based and the nitrate based fertilizers into a single, high-nitrogen fertilizer. An odorant(s) with a low odor threshold is also added during or after coating to make it possible to detect the fertilizer by smell. Pleasant-smelling and non-toxic ester-based or similar odorants can be detected by humans in the parts per billion range and it is likely that military and police canines can be trained to detect such additives at even lower concentrations. Importantly, addition of a low-odor-threshold odorant facilitates detection without the need for sophisticated or cumbersome equipment.